Measuring via Synthezed (digital) Linkwitz Transform? - Page 2 - Home Theater Forum and Systems -

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post #11 of 14 Old 09-30-14, 10:50 AM Thread Starter
Join Date: Apr 2013
Posts: 12
Re: Measuring via Synthezed (digital) Linkwitz Transform?

Back again,

I looked in REW. As has been suggested, the only way to input LT response is via REWs House curve feature. However, it still can only be imported by means of .txt.

My question is how to create .txt format EQ. I'm not aware of any programs that allow to create then export LWT as .txt.

There are various LT calculators online, most are spreadsheets and so I doubt any can export as .txt response.

@ nate - thanks for suggesting JRiver, but I intend to use an alternative for the time being
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post #12 of 14 Old 09-30-14, 01:16 PM
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Re: Measuring via Synthezed (digital) Linkwitz Transform?

Entering a house curve into REW is easy if you know how to create a text file. The instructions for the file contents is found at REW "Help/Preferences/House Curve". Just enter the XY points of the LT curve you want to create into the text file. You can use a spreadsheet to create the XY points and expert them to the text file or just read them from the WinISD chart you created and manually enter them.

Load the resulting text file into "Preferences/House Curve". Be sure to set the "Preference/Equalizer/Slope" settings to "0" instead of the default. Otherwise the house curve you entered will be impacted by the slope settings; we don't want that.

To create the filter settings needed using REW I suggest a loopback measurement of the sub output that includes the LP/HP filters if that is possible. If the house curve is your final curve (#3) REW can calculate the filters needed directly from that. You could set a shelf filter manually and then let REW calculate the remaining peak filters, but looking at your target shape, I don't think a shelf filter is called for. If you can't measure a loopback with HP/LP filters active then the appropriate changes to the house curve should be made.

Even if you aren't doing any measuring with REW and instead just calculating filters sans the HP/HP filters you can do that also. It is just necessary to define the house curve appropriately and to import a flat measurement file for the REW for calculation.
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post #13 of 14 Old 10-03-14, 05:55 AM Thread Starter
Join Date: Apr 2013
Posts: 12
Re: Measuring via Synthezed (digital) Linkwitz Transform?


I now realize APO EQ is incompatible with XP!
Looks like I shall have to use REWs House curve. I will get round to REW eventually but I'm stuck at this stage which is prior anything to do with REW:

Creation of .txt (for importing/use with REW).

I discovered the UniBOX spreadsheet floating about online. It has a .FRD export feature built in and these .FRD files can be opened with notepad. It has the following headers:

Frequency[Hz] Level[dBspl] Phase[Deg]
Example: 10.0000 57.5817 171.0299

I've attached an .FRD file to this post.
It's in .txt format because site wouldn't allow upload of .FRD - it's the same anyway.

jtalden, You say to export from winISD its a case of taking X/Y (Freq./Level) plots from a graph and transferring across to devise a curve. Is it really as easy as picking random plots from a graph?
Shouldn't considerations be made to the Q factor also (for example)?

Thanks again.
Attached Files example.txt (15.9 KB) 

Last edited by giro1991; 10-03-14 at 06:02 AM.
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post #14 of 14 Old 10-03-14, 11:12 AM
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Re: Measuring via Synthezed (digital) Linkwitz Transform?

Yes, it can be done manually that way. But...

If the attached curve were the house curve you wanted, it can be imported as is. Just load it into REW as the house curve. Below, I did that so show you the result. You must adjust the house curve settings as shown or the curve will be distorted as the settings dictate. Also, a house curves is normally entered with the SPL levels being relative to 0dB as shown in REW Help. Since your file is at ~93B you have to adjust it accordingly. I just told REW to reduce the target level to 0 dB instead of the default 75dB. The curve then fell right at ~93dB as shown. [An option is to edit the text file to reduce the SPL level by ~93dB. The third column in the file can be deleted if you want because the phase is not used in the house curve. REW just ignores it, so it can also just be left as is - no problem.]

I also imported the same file as a measurement. It is also shown on the chart. So the chart shows the same response for both the house curve and the measured response. Since I moved the house curve down 75dB from ~168dB to the same level as the imported response, the 2 traces overlap each other. The legend shows that both are being plotted. I maybe should have offset them a little. If this were the current actual vs the target house curve an REW filter calculation would indicate that no filters are needed.

Measuring via Synthezed (digital) Linkwitz Transform?-eq-shot2.png

Your question about the Q factor confuses me. We are not entering filters into REW (at least not yet). We are entering the house curve and the response that we want to modify (in you case a flat curve modified by the LP/HP filters should be measured/entered). REW then can calculate the filters needed to modify that "actual response" into the target house curve response.

It is very likely that I am still not understanding you situation though.

I finally surmised that you wanted to calculate filters needed to create an LT electrical response as modified to include the HP/LP filters, i.e. your curve#3:
To do that we could:
> Enter curve #3 as a house curve. [The target response of the voltage to the SW.]
> You have the HPF and LPF filters implement in an external circuit now so a loopback measurement using REW will give your current electrical response. It would be a flat bandpass with the the HP / LP filters applied the response. It would not have the peak shown in #3, the house curve.
> Allow REW to calculate the filters needed to modify the measured response to match the house curve response.
> Enter those filters into an EQ unit (APO or other) and activate it.
> Measure the loopback again to confirm the measurement now follows the house curve.

You have not confirmed if you intend to measure a voltage loopback of your system using REW, or are just using REW to do filter calculations based on imported files. Which is it? Either can be done.
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